1. Field of the Invention
This invention relates to polyester multifilament yarn with high modulus and low shrinkage particularly useful for the textile reinforcement of tires. The yarn of the invention provides high treated cord tenacity while maintaining or increasing treated cord dimensional stability when compared to prior art yarns. A process for production of the multifilament polyester yarn is an aspect of the invention.
2. Description of the Prior Art
Polyethylene terephthalate filaments of high strength are well known in the art and are commonly utilized in industrial applications including tire cord for rubber reinforcement, conveyor belts, seat belts, V-belts and hosing.
Continued improvement in high strength industrial yarns particularly suited for use as fibrous reinforcement in rubber tires is an ongoing need in the industry. In particular, the improvement of treated cord tenacity and dimensional stability are desired objectives. U.S. Pat. No. 4,101,525 to Davis et al. provides an industrial strength multifilament polyester yarn with high initial modulus and low shrinkage. Although Davis et al. does not provide treated cord data, it is commonly known that compared to conventional tire cords such yarn provides a reduced tenacity when the yarn is converted to the treated tire cord. Additionally, rapid cooling of the filament immediately after emerging from the spinneret can result in excessive filament breakage and thus yield yarn with poor mechanical quality. U.S. Pat. No. 4,491,657 to Saito et al. discloses high modulus, low shrinkage polyester yarn, but requires a low terminal modulus to achieve good yarn to treated cord conversion efficiency for such dimensionally stable yarns. The low terminal modulus is carried over into the treated cord and results in a lower tenacity than the high terminal modulus cords of the present invention. Also, as shown in FIG. 8, the process of Saito et al. requires high spinning speeds, which makes it difficult to process on-panel, i.e. a continuous spin-draw process.